Soul of Theros is a mythic Creature — Avatar card from Mystery Booster 2 (MB2), collector number 19. Current market price: $0.30, TCGplayer market prices via Scryfall.
Vigilance {4}{W}{W}: Creatures you control get +2/+2 and gain first strike and lifelink until end of turn. {4}{W}{W}, Exile this card from your graveyard: Creatures you control get +2/+2 and gain first strike and lifelink until end of turn.